A seizure is a paroxysmal event due to abnormal, excessive, hypersynchronous discharges from an aggregate of central nervous system (CNS) neurons, while epilepsy is a condition in which a person has recurrent seizures due to a chronic, underlying process. Experimental and clinical data indicate that the occurrence of repeated seizures can lead to an epileptic condition. It is therefore of great interest to identify possible pharmacological treatments for seizures, and the time-frame in which such treatment is effective.
Epilepsy is a brain disorder characterized by, periodic and unpredictable seizures caused by the rhythmic firing of large groups of neurons. The behavioral manifestations of epileptic seizures in human patients range from mild twitching of an extremity to loss of consciousness and uncontrollable convulsions. Up to 1% of the population is afflicted, making epilepsy one of the most common neurological problems. The abnormal activity associated with epilepsy generates plastic changes in cortical circuitry that play a part in the pathogenesis of the disease. The importance of synaptic plasticity in epilepsy is indicated most clearly by an animal model of seizure production called “kindling.” Over a period of time, a weak stimulus that initially had no effect will eventually cause full-blown seizures. This phenomenon is essentially permanent; even after an interval of a year; the same weak stimulus will again trigger a seizure.
Research has focused on where seizures originate and the mechanisms that make the affected region hyperexcitable. Evidence suggests that abnormal activity in cerebral cortex foci provide the triggers for a seizure that then spreads to other synaptically connected regions. Epileptic seizures can be caused by a variety of acute or congenital factors, including cortical damage from trauma, stroke, tumors, congenital cortical dysgenesis, and congenital vascular malformations.
No effective prevention or cure exists for epilepsy. Pharmacological therapies that successfully inhibit seizures are based on two general strategies. One approach is to enhance the function of inhibitory GABAergic synapses; the other is to limit action potential firing by acting on voltage-gated Na+ channels. Commonly used antiseizure medications include carbamazepine, phenobarbital, phenytoin, and valproic acid. These agents must be taken daily, and only inhibit seizures in 60-70% of patients.
A number of processes are thought to contribute to the development of epilepsy including enduring increases in excitatory synaptic transmission, changes in GABAergic inhibition, neuronal cell death and the development of aberrant innervation patterns in part arising from reactive axonal growth. It has also been suggested that activities of integrin class adhesion receptors play roles in each of these processes by stabilizing activity-induced increases in synaptic strength and excitability. These same adhesion proteins and proteases play critical roles in axonal growth and synaptogenesis including processes induced by seizure in adult brain (Gall et al. (2004) Adv Exp Med Biol. 548:12-33).